Little effort has been made to investigate the potential of web programs aimed to support the mental wellbeing of adolescents in school environments in middle-income countries. A quasi-experimental feasibility study was conducted in Thailand with adolescents (N = 180) in three conveniently sampled high schools and with teachers (N = 12) who acted as program tutors. The web program was used in small groups, independently, or it was not used at all. No statistically significant changes were found between the groups regarding depression, stress, or satisfaction. Differences between program users (n = 61) and non-users (n = 48) were not significant. Acceptance was higher among adolescents who used the program independently (n = 40, 73% vs. n = 21, 39%; p = 0.001). Usability feedback did not differ between the groups. Support should be provided in order for programs to be potentially used. More information is needed regarding factors associated with the use of web programs.